Study Of Photocarrier Dynamics In Monolayer ReSe₂ And Their Heterostructures

The photocarrier behavior in two-dimensional materials plays an important role in the properties of optoelectronic devices.At present,the physical mechanism and model of the carrier transfer process and the band alignment in heterostructure composed of ReSe₂ and different materials are still controversial.In this paper,we study the ReSe₂ and its heterostructures by using transient absorption pump-probe technique.The main innovations of this paper are as follows:1. The carrier dynamics of ReSe₂ was studied by transient absorption technique.The differential reflection signal of ReSe₂ has the 4-fold symmetry,indicating that ReSe₂ has anisotropic transient absorption characteristics,we attribute the 4-fold symmetry to the potential compensation between the maximum absorption coefficient and the minimal transient absorption response along the parallel and perpendicular directions.After normalization of the signals at different angles,it is found that all the signals overlap well,indicating that the photocarrier dynamics in different crystal directions are the same.2. The transient absorption measurements were performed to study the dynamics of charge transfer,indirect exciton formation,and indirect exciton recombination in monolayers Mo S₂-ReSe₂ heterostructure.Only the heterostructure detects the signal,which proves that the electrons are excited in ReSe₂ and sequentially transferred to Mo S₂.It proves that the hole can be transferred from Mo S₂ to ReSe₂.The effects of the holes injected directly in Re S₂ or transferred from Mo S₂ were studied.The efficiency of electrons and holes in the same layer in inducing differential reflection signals was studied.3. A monolayers WS₂-ReSe₂ heterostructure has been prepared,the quenching of the PL peak proves the existence of charge transfer.Under different pump-probe conditions,the existence of the detected signal indicates that the electrons in the ReSe₂ can be transferred to WS₂ and the conduction band minimum is located in WS₂.The first experiment proved that the WS₂-ReSe₂ heterostructure is type II band alignment,in which the conduction band minimum is located in WS₂.It is inconsistent with the conclusion that Li Ming et al predicted the WS₂-ReSe₂ heterostructure is typeⅠband alignment and the conduction band minimum is located in ReSe₂ by first-principle calculation.